Background: Injection of ultrasound contrast agents, in conjunction with contrast specific imaging techniques, is increasingly accepted in clinical use for diagnostic ultrasound imaging. As microbubbles contrast agents appear to be ideal pure intravascular tracers to enhance the vascular lumen and more important to assess the dynamic spatial and temporal heterogeneity of the microvasculature, contrast enhanced ultrasound (CEUS) provides a unique opportunity for new application especially in vascular imaging. CEUS of the carotid artery has been introduced as a non-invasive technique to improve detection of carotid atherosclerosis and evaluate the presence of plaque vascularity (vasa vasorum). As the proliferation of intraplaque and adventitial vasa vasorum (neovascularization) are inherently linked with the atherosclerotic plaque development, plaque inflammation and vulnerability, direct visualization of intraplaque neovascularization by CEUS has emerged as a new marker for plaque instability.